1. Field of the Invention
The subject invention generally pertains to the ventilation of buildings and more specifically to a ventilation system that delivers a generally constant airflow rate regardless of changes in the pressure differential between the indoor and outdoor air.
2. Description of Related Art
Heating ventilating and air conditioning systems, or HVAC systems, often include a blower and a heat exchanger for providing air that is heated, cooled, dehumidified, or conditioned in some way to meet the needs of a building and its occupants. Supply air ductwork can be used for conveying the conditioned air to various rooms of the building. After the conditioned air (supply air) enters and circulates through the rooms, the blower draws the used air (return air) back out of the rooms via a network of return air ducts. The blower then forces the air back across the heat exchanger for reconditioning.
In some cases, a tightly sealed home or building may create a stale indoor atmosphere due to an inadequate exchange of indoor and outdoor air caused by a lack of forced or natural ventilation. To maintain the freshness or quality of the indoor air, an HVAC system may include additional ductwork and inlet dampers that permit a limited amount of outdoor air into the building. Under steady state conditions, the incoming fresh air displaces an equal amount of more stale indoor air. The displaced indoor air can escape the building by natural leakage through windows, doors, or other incidental cracks or openings in the building.
Although sophisticated ventilation systems can be custom designed and configured for specific commercial and industrial buildings, such an approach may be impractical for homes or smaller residential buildings that may be no more than three stories above ground. Even after determining the ventilation airflow requirements of a particular home, it may be difficult to properly set up or adjust a conventional ventilation system to meet those requirements. Airflow measuring instruments and trained service technicians may be needed to ensure that the system is properly set up for providing adequate ventilation. Some attempts, however, have been made to simplify the job of adjusting or setting up a ventilation system for residential buildings.
Honeywell, for instance, provides a Y8150A Fresh Air Ventilation System that allows a user to dial in a home's square footage and the number of bedrooms. The system then calculates the required ventilation rate based on ASHRAE Standard 62.2. To achieve the required ventilation rate, however, the system is first calibrated for the particular building in which the system is being installed. The calibration process determines the flow rate when the system's damper is wide open. By knowing the wide-open flow rate, the Honeywell system can cycle the damper open and closed to provide, on average, the required ventilation rate. Such a system, however, has a few drawbacks.
First, the Honeywell system relies on the building's main HVAC blower for drawing ventilation air into the building. Since such a blower is normally much larger than that which would be needed for ventilation alone, energy is wasted during periods when only ventilation is needed.
Second, while calibrating the system, the main HVAC blower may be operating at high or low volume depending on various factors such as whether the HVAC is operating in a cooling or heating mode at the time of calibration. Later, during normal operation, the blower's volume may change from what it was during calibration, thus the actual ventilation rate may be off significantly.
Third, it does not appear that the Honeywell system accounts for changes in the static pressure differential between the indoor and outdoor air. Thus, the actual ventilation flow rate may be affected by opening and closing windows and doors, operating bathroom exhaust fans, operating kitchen exhaust fans, etc.
Consequently, a need exists for a standalone ventilation system that is easily configured for various buildings.